Rotavirus Prevents the Expression of Host Responses by Blocking the Nucleocytoplasmic Transport of Polyadenylated mRNAs

Abstract

bRotaviruses are the most important agent of severe gastroenteritis in young children. Early in infection, these viruses take over the host translation machinery, causing a severe shutoff of cell protein synthesis while viral proteins are efficiently synthesized. In infected cells, there is an accumulation of the cytoplasmic poly(A)-binding protein in the nucleus, induced by the viral protein NSP3. Here we found that poly(A)-containing mRNAs also accumulate and become hyperadenylated in the nuclei of infected cells. Using reporter genes bearing the untranslated regions (UTRs) of cellular or viral genes, we found that the viral UTRs do not determine the efficiency of translation of mRNAs in rotavirus-infected cells. Furthermore, we showed that while a polyadenylated reporter mRNA directly delivered into the cytoplasm of infected cells was efficiently translated, the same reporter introduced as a plasmid that needs to be transcribed and exported to the cytoplasm was poorly translated. Altogether, these results suggest that nuclear retention of poly(A)-containing mRNAs is one of the main strategies of rotavirus to control cell translation and therefore the host antiviral and stress responses.

Rotavirus NSP3 Is a Translational Surrogate of the Poly(A) Binding Protein-Poly(A) Complex

“…The NSP3 RNA-and eIF4G-binding domains (RNA-BD and 4G-BD, respectively) have been proposed to function independently, with the enhancement of viral mRNA translation due to NSP3 instead resulting from viral mRNA protection by the RNA-BD, whereas 4G-BD is involved in inhibiting host poly(A) mRNA translation (18). In the same vein, the translation of polyadenylated mRNAs introduced directly into the cytoplasm was not inhibited by rotavirus infection, in contrast to mRNAs synthesized in the nucleus, suggesting that a reduction in mRNA nuclear export rather than translation inhibition accounts for the rotavirus-mediated extinction of host protein synthesis (19). However, using an in vivo assay, we recently showed that the NSP3-dependent protection of viral mRNA from degradation was not sufficient to enhance translation and that NSP3 RNA-BD and 4G-BD did not work separately (M. Gratia, unpublished data).…”

“…Our results suggest that the RF and RRV strains differentially impact one or more of these steps and that the inhibition of translation by NSP3 is not the sole factor involved in shutting down cellular protein synthesis. Another explanation is that the numerous viral mRNA copies present during infection (19,35) simply titrate away translation initiation factors and render them inaccessible to host poly(A) mRNAs. Thus, the inhibition of cellular polyadenylated mRNA translation during rotavirus infection would be more likely to result from the high level of viral mRNA translation facilitated by NSP3 rather than by the direct exclusion of cellular mRNAs from translation initiation complexes.…”

“…4. It can be noted that a slight increase in luciferase activity was observed 1 to 2 h after infection, probably due to a transient inhibition of the proteasome consequential to the activation of the unfolded protein response triggered by rotavirus infection (19,32). RF required 3.5 h and RRV required 6 h to inhibit 50% of the cellular protein synthesis, and whereas RF reduced expression to 10% of the initial value after 8 h of infection, RRV reduced expression to just below 50% (Fig.…”

A paradox of transcriptional and functional innate interferon responses of human intestinal enteroids to enteric virus infection

“…Together, these data suggest that the transcriptional regulatory pathways upstream of IFN induction remain at least partially intact in these models. However, rotavirus can also inhibit host responses by decreasing translation of host mRNA through multiple mechanisms primarily via the protein NSP3 (24,(79)(80)(81). Although these mechanisms do not selectively antagonize IFN, production of IFN protein is likely reduced when there is a global decrease in host translation.…”

Sequestration Strikes Again: Rotavirus-Induced Accumulation of Cellular Transcripts in the Nucleus Inhibits Host Protein Translation

“…The recent article by Rubio et al identifies the effects of rotavirus-induced cytoplasmic poly(A)-binding protein (PABPC) nuclear accumulation and demonstrates that they play key roles in the inhibition of host protein synthesis in infected cells [1]. Host cell mRNAs are transcribed in the nucleus and are usually modified to contain a 5´ cap structure and a 3´ poly(A) tail.…”